- A moderate sized group (ca. 40 genera & 800 spp.)
- Unicellular flagellates
- Primarily freshwater, but important in some marine environments
- Many are heterotrophic (saprotrophic or phagocytic)
- Also called Euglenozoa, euglenoids, euglenophytes
- Distinctive cell walls composed of spiral strips, termed the "pellicle"
- Structure & metabolism
- Two anterior, unequal flagella, rooted within a canal, the ampulla
- This latter term refers to the flask-like shape of the canal, with
a distinct canal and internal reservoir
- The shorter flaellum is often very short, and may not emerge from
- The longer flagellum extends forward, and is covered by two distinct
kinds of fine hairs (not mastigonemes)
- Eyespot is in cytoplasm near the canal, not in plastid
- Often easily visible with light microscope
- Composed of carotenoid globules, surrounded by individual membranes
- Not associated with chloroplast
- A swelling at the base of the longer flagellum is thought to act as
- A contractile vacuole is present at the apical end of the cell, empties
- Pellicle lies within the cytoplasm, at the surface of the cell
- Composed of spiral strips of protein that overlap slightly
- In many species, these can slide with respect to each other
- This produces a distinctive mobility called euglenoid movement, or
- Many species are rigid when swimming in plankton, but rely on metaboly
when on solid surfaces
- Other species are entirely rigid, but spiral pellicle is still present
- Muciferous bodies secrete mucilage, which may make a thin or thick layer
over the cell
- Nonmotile cells embedded in a thick layer of mucilage are considered
to be palmelloid
- Some species have a lorica, or hard surrounding shell
- Nucleus with permanently condensed chromosomes
- Mitosis is closed
- Spindle is essentially entirely within nuclear envelope
- Nucleolus is persistent throughout mitosis
- Cytokinesis starts with replication of basal bodies and flagella
- Nucleus migrates to apical end of cell, and basal bodies associate with
developing spindle poles
- Mitosis is followed by longitudinal furrowing of cell
- Pellicle strips twist in two spirals, so that cell divides without disrupting
spiral arrangement-- very elegant
- Chloroplasts (if present) is thought to be a secondary plastid derived
from green algae
- Typically multiple chloroplasts per cell
- Surrounded by three membranes, without a CER or nucleomorph
- Thylakoids in groups of three, without a girdle lamella
- Pyrenoids may be present, and in many taxa are stalked and cluster
into a single mass
- Pigmented with Chlorophylls a and b
- Main secondary pigments are beta-carotene, neoxanthin, and diadinoxanthin
- Minor pigments include echinenone, diatoxanthin, and zeaxanthin
- Imported proteins are targeted first to ER, and subsequently to chloroplast
- Some nuclear-encoded, chloroplast expressed genes, including rubisco
small subunits are translated and imported into the plastid as a polyprotein.
- Makes sense in terms of secondary origin of plastid
- Food storage outside of plastid, as paramylon (a beta-1,3 linked glucan)
- Sex has not been observed, and it has been argued that euglenoids diverged
from the eukaryotic main series prior to the evolution of sex. It is also
possible that they are descended from sexual ancestors, but have lost sex,
or that they do reproduce sexually, but do so discreetly.
- Related to Kinetoplastida (trypanosomes), but other phylogenetic affinities
- In SSU rRNA analyses, show up as a long branch outside of crown group,
but this placement is increasingly suspect
- A standard research organism, used as model system and genetic system.
- Not a good model for plants or animals, but an extremely interesting
- Important in early demonstration of plastids as endosymbiotic organelles
- Euglena grown at high temperature will lose its plastids
- This provided early evidence that plastids were "special"
- They cannot be synthesized de novo, i.e., once lost, they
cannot be rebuilt
- Even photosynthetic euglenoids are typically capable of heterotrophic
- In studies of the herbicide diquat, Euglena was found to grow
slightly faster in presence of high concentrations of the
- Chloroplasts were completely inactive, but Euglena was growing
heterotrophically, using diquat as food
- Structurally very similar to Euglena
- Heterotrophic and unpigmented, but does have plastids
- Lives in frog cloacas
- Trachelomonas -- loricate, with flagella emerging from a pore at
the apex of the lorica
- Colacium - sessile cells attached to a branching network of stalks,
the stalks being attached at the anterior ends of cells. Can release from
the stalk, swim around, then settle and start a new colony.
- Phacus -- free swimming, with rigid, flattened cells.
- Peranema -- colorless, perhaps primitively so. Feeds actively by
either phagocytosis or myzocytosis.
- Petalomonas cantuscygni -- according to rRNA studies, branches
before the divergence between Euglenophyta and Kinetoplastida.
- Often found in highly eutrophic environments
- Ditches and ponds near cow pastures, hog lots, chicken farms, etc.
- A thick green or red scum on the surface of the water is often from a
- Mud flats (another highly productive environment) are also good euglenoid
- Very few euglenoids have been grown in axenic culture, and euglenoid culture
media are generally very nutrient rich
- Economic Importance
- Although an indicator group for disgusting environmental conditions, euglenoids
are generally harmless
Required Reading: VdH: Chapter 17
Hallick, R.B., L. Hong, R.G. Drager, M.R. Favreau, A. Monfort, B. Orsat, A.
Spielmann, and E. Stutz. 1993. Complete sequence of Euglena gracilis
chloroplast DNA. Nucl. Acids Res. 21:3537-3544.
Stevenson, J.K., and R.B. Hallick. 1994. The psaA operon pre-mRNA of the Euglena
gracilis chloroplast is processed into photosystem I and II mRNAs that accumulate
differently depending on the conditions of cell growth. The Plant J.
Triemer, R.E. 1997. Feeding in Peranema trichophorum revisited (Euglenophyta).
J. Phycol. 33:649-654.